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MG MGB Technical - Best Cam

I'm going to be rebuilding an 18GB engine. With a +60 rebore and a Stage 2 head and improved exhaust, K&N filters etc. However, the original cam is shot.

Which cam should I buy to make the best of the other improvements I'm making.
Iwan Jones

Iwan,

If you can put up with a lumpy idle then go for the Piper HR 285 - if you want something more tractable at low revs then an HR270
Chris Betson

Iwan-
Best all-around street cam? Piper 270.
Steve S.

Iwan & steve,

BP270's are diferent to HR270's
Chris Betson

I rebuilt an MGB engine to a similar spec, 60thou overbore, large valve head, 1 3/4 SU's i had a Kent 717 cam, this needed valve pockets machined in the head, it had a lumpy idle and didn't really start pulling to 2500 rpm, fuel economy really went down as well, getting 15mpg round town (not driven hard). My friend owns an MG Centre, he had a B in still on inch and a half Carbs with the Piper 285 cam in, the engine really was impressive. Tick over was good and it really pulled hard from low down.
Ian Sanders

I just switched from a BP285 to an Elgin 6707-18. Much better. More power down low, more power up high, idles properly now...

It's magic. Less tappet noise now, too. Dema Elgin's secret? Gnomes, apparently.

Rob
Rob Olsen

Iwan-
I'm re-building an 18GH engine with the same specs you mentioned, .060 pistons, stage two head, and I am upping it to 9.5/1, and will use original SU carbs, K+N filters and Peco exhaust. I dropped a line to Piper, and they recommended the BP270. I am led to understand that it is a refinement over the HR, and is both driveable with good power. I'm sure the BP285 is has more high range power, but I don't plan to race...just zing along the back roads.
Thomas Lennon

Iam,

I'm running a Kent 717 with dual HS6 (1 3/4) carbs on a 1950cc engine. The mileage is 22 city and 25-27 highway...the idle is neither smooth nor lumpy at 850 rpm and it pulls from 1500 through 5100 (peaks at 105 hp at 4750 according to a rolling road test)

What tappet settings are you using...mine are adjusted at 16 thou intake and 17 thou exhaust..

rn
RN Lipow

Hiya,

Careful of setting the lash too tight with the 717, you could induce early burn out of the exhaust valves at less than the stated 24 thou. The 717 has very long, gentle opening ramps and as such is not loud with the 'loose' clearances.
We tend to find the BP285 a little 'boring' compared to the original HR285 profile. The HR pulls cleanly from just off idle. The 717 is a real torque buster although it does lack higher rpm power. Horses for courses I suppose.

Peter
peter burgess

along with other mods i have a Kent 714 cam....I was wondering how does this shape up against the Piper BP270....I am confused by all of these numbers..I thought they all realted to the timing of the said cam...but Kent use a numbering system that does not seem to relate to that.

I am happy with the engine...but what should I use if and when I rebuild the engine?
ian holliday

Has anyone had any experience with APT's VP-12 cam? My current mechanic recently put this in my engine after the Crane cam (the "performance" one from Moss) began chewing up the lifters (and consequently itself) less than 2000 miles after the rebuild (which had been done by another shop). Since my car is currently "hibernating" in the shop for the remainder of the Canadian winter, I have no first-hand experience yet. My engine is fully worked over, with opened up head, higher compression, and the Maniflow intake and exhaust manifolds (my former shop did a good job on these things).

The VP-12 is APT's "fast road" cam. I would imagine that it was developed by David Vizard, so it should probably be good, but I've never myself seen anyone comment on it on this BBS.

By the way, I am very grateful to Doug Jackson's web pages for the warning about the Crane cam. As a result, when my valves began to need adjustment every 500 miles starting at the 1000 mile mark, I suspected what the problem was long before I would have otherwise. It was already too late to avoid the cam/lifter damage that did occur, but I imagine I at least avoided worse destruction.
David Cushman

Ian,

The Kent 714 is a Leyland rally profile designed for use on loose surfaces and, as such, doesn't have a ferocious power delivery so it gives predictable performance. The camshaft delivers less maximum power and less lower rpm power than the standard cam, although it allows the engine to rev to around 6500 rpm with usable power. The BP270 is a milder cam which enhances midrange torque and gives an enhancement to top end bhp and more useable rpm compared to the standard cam. The BP270 is much better for road use.

Peter
peter burgess

I will vouch for Dema Elgin's cams also. I installed one of Dema's cams as part of my engine rebuild and the power and torque increases are huge, yet the engine will idle at 1,000 RPM all day. There is a little bit of "lump" in the cam at idle, but this is his "hottest" MGB cam that is not a full race cam.

You can get to Dema's website through British Automotive's website at www.mgbmga.com. There is a link there and I believe that one of the technical articles on that site lists out the cams that Dema makes as "standard" for the MGB.
Ron Kluwe

Peter
Thanks for your information…. the engine was built by Moto-Build back in 94. I use the car for Production Car Trials so the “loose surfaces design” would ring true. It seems that the engine does rev up into the red line.... way past the yellow section. Because I abuse the car so much I may be looking at another engine rebuild soon.
ian holliday

Whilst on the subject of cams, should I fit a different cam to the factory standard on my Fed Spec LE now that I am changing to HIF4's, and dispencing w/ the emmission stuff. The pistons are low compression and I wondered if they should be replaced also.
Desired result is a perky sporty car w/ a decent tickover, not a bucking bronco.
Mark Smith

Mark ….the short answer to your question is yes. I would advise a chat with either Chris Betson or Peter Burgess (emails given above)about some changes to your car. They will advise you on the best changes to make.


Ian

PS my car is very tractable, I love the way is surprises some but at the same time I would not call it a bucking bronco.
ian holliday

I'll put in a third recommendation for Elgin's camshafts. My head has been modified to Burgess' D.I.Y. specs, with three angle valves, the bores are .040 over and I'm running old 1.5 inch S.U. carbs. With Elgin's near stock grind my engine has tons of torque down low and revs cleanly to redline. It will idle below 1000 rpm and it will pull 3rd gear from 1500 rpm.
And If you drop the clutch at 4000, those skinny little tires just go up in smoke. I couldn't be happier.
Chris
'66 roadster

and do dial in whatever cam you buy with a dial indicator and timing ring. most important.
Chris Birdwell

Since on the subject of cams and Peter is here, I have a question. My '78s engine has been set up as follows:
0.060 overbore, head re-worked to somewhere between Peter's DIY spec and rally spec with 1.625 intake valves, head shaved 0.020, and BP270 camshaft. Pistons are standard dish for "78 as I recall. For carburation it presently has a radically re-worked ZS single carb and manifold, and the exhaust is the Falcon SS big bore. I will be converting to twin 1.75" SUs and the Peco header. WIll the BP270 camshaft need to change to accommodate the big SU carbs? Should I need different jets?
Gerald O'Docharty

Iwan,

I am using a Kent 717 on an +0.040" overbore with stage 3 (big inlets) head and HS6's.

Idle is hopeless, even at 1000 rpm (although the carbs probably don't help). It doesn't pull that well below 3000rpm, but still better than a bog-standard engine. It pulls like a train from 3000 to 6000rpm+ (the bottom end is lightened/balanced) and sounds great. Peak power is at about 5500rpm according to the rolling road.

You have to get the carb/cam/head/timing combination just right!

Neil
Neil

Hiya,

Gerald - A Piper HR285 cam would work well, you would have to run around 9.75:1 CR to get the best from the setup you have. 20 thou doesn't seem to be much off the head...what cr do you have at present?

Neil - did you time your camshaft in? The 717 is a torquey cam that should pull strongly from low rpms and not rev too high..say 5500rpm.

Peter
Peter Burgess

Peter,

Yes I did, and have recently had the engine apart to check the timing!

I reckon that the big inlet valves and HS6's are probably screwing up the idle and low speed torque.

Neil
Neil

Hiya Neil,

The larger carbs always make the lower rpm seem 'soft', the gas velocities are lower and the fuel gets more of a chance to drop out!


What sort of compression ratio are you running?

Peter
Peter Burgess

How much valve lift will an 1800 take before the block needs to be notched? I imagine it is different depending on the head being used, but if you could include that too it would be interesting. I've contemplated running higher lift rockers like TSI or BA sells, but am afraid of this complication. I'm used to checking valve clearance to piston and so forth, but currently do not need a shortblock rebuild right now and would like to avoid this with the deck surface on the block.

TIA
Luke

For me specifically I have OEM type pistons with a late head.
Luke S.

Hiya Luke,

The amount of valve lift will depend on the distance from the exhaust valve face to the block, which will be dictated by the amount skimmed from the head.

Unskimmed 18v chambers are approx. 10 mm deep. The valve face maybe 1 to 1.5 mm proud of the chamber roof. Say the valve is 1.5 mm proud...this leaves 8.5 to the head face. Add the gasket thickness, say 1 mm, giving 9.5 mm ..... approx 380 thou. If your cam train is perfect valve lift will be 365 thou....not enough clearance left for safety, which is why the 18v blocks have cutouts for the exhaust valves.

Pre 18v heads are 11 mm deep, which, with the above scenario would give 420 thou clearance.

With 18v block cutouts, 2mm (80 thou) off the head should be safe, however, that would be a lot to skim off a head as each mm is approx equal to 4 cc!
The amount to skim off would depend on the fitted height of the pistons and the piston dish.

Hope this helps,

Peter
Peter Burgess

Peter,

compression ration is 9.75:1

Neil
Neil

Hiya Neil,

It should run sweetly at that cr .... do you think the head is working as it should? Have the inlet ports been enlarged, was it modified with three angle valve seats?

Peter
peter burgess

This thread was discussed between 26/01/2002 and 02/02/2002

MG MGB Technical index

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